The present invention relates to resonators used in RF communication and other equipment. More specifically, the present invention relates to a dielectric resonator configured to have a lowest resonant frequency in the HE0xcex3xcex4 mode.
Dielectric resonators are smaller than air cavity resonators having equivalent resonant frequencies because wavelengths in the dielectric resonator are divided by the square root of the resonator""s dielectric constant. In addition, reactive power need not be stored strictly inside the dielectric resonator, and fractional modes of resonance are possible.
Unfortunately, for many applications conventional dielectric resonators are still undesirably large and/or made from exotic materials that are too costly. Mass market portable RF communication devices represent one example of such applications. While most electronics equipment benefits from smaller, less expensive components, portable RF communication devices receive particular benefit because of a heightened need to be as small and lightweight as possible, while being as inexpensive as possible to effectively compete in a highly competitive marketplace.
U.S. Pat. No. 6,169,467, entitled xe2x80x9cDielectric Resonator Comprising A Dielectric Resonator Disk Having A Hole,xe2x80x9d and having a common inventive entity and assignee herewith is incorporated herein by reference. This patent teaches a TE0xcex3xcex4 mode dielectric resonator, where xe2x80x9cxcex3xe2x80x9d indicates a fraction of periodicity in the radial direction, and xe2x80x9cxcex4xe2x80x9d indicates a fraction of periodicity in the axial direction. This TE0xcex3xcex4 mode resonator achieves a relatively small size due, in part, to the fractional mode of resonance in two dimensions while simultaneously achieving an excellent quality factor (Q). Unfortunately, to achieve the excellent quality factor sacrifices were made that resulted in a larger size and more expensive configuration than would be desired for many applications. Moreover, while most all applications benefit from a quality factor as high as possible, some applications do not require an excellent quality factor and can tolerate merely a good quality factor.
A conventional practice in using dielectric resonators is to configure the resonator to resonate in a TE mode within a cavity and to incorporate an adjustable tuning device. Conventional tuning devices have an adjustable position relative to a dielectric resonator within a conductive cavity. The use of a conductive cavity having walls positioned some distance away from the dielectric resonator is useful for maintaining as high a quality factor as possible, but increases size and cost accordingly. In some examples, the tuning devices are conductive members, but conductive tuning devices are not desired because they are lossy and diminish the quality factor of the resonator.
In other examples, the tuning devices are dielectric members having as high a dielectric constant and quality factor as possible. A high dielectric constant is desired to achieve an effective tuning range. Often, a dielectric tuning member is made from the same material as the dielectric resonator being tuned, but a material having an even greater dielectric constant would be desirable to increase tuning range. The use of a common dielectric material for the resonator and the tuning member is undesirable because dielectric materials tend to be expensive, and particularly expensive where small resonator size is a goal and more exotic dielectric materials having higher dielectric constants are being used. The use of a dielectric tuning member having a greater dielectric constant than the dielectric constant of the dielectric resonator would be even more expensive and therefore undesirable.
Accordingly, it is an advantage of the present invention that an improved HE0xcex3xcex4 mode dielectric resonator is provided.
Another advantage of the present invention is that a HE0xcex3xcex4 mode dielectric resonator is provided which achieves a good Q in a smaller volume than required by a TE mode dielectric resonator or other HE mode dielectric resonators at the same frequency.
Another advantage is that a tunable HE0xcex3xcex4 mode dielectric resonator is provided.
Still another advantage is that a tunable HE0xcex3xcex4 mode dielectric resonator is provided wherein tuning is accomplished at very low cost and with substantially no deterioration in quality factor.
The above and other advantages of the present invention are carried out in one form by a tunable HE0xcex3xcex4 mode dielectric resonator. This resonator includes a disk formed in the shape of a cylinder having a diameter D. The disk is formed from a first dielectric material configured to exhibit a dielectric constant ∈r. The disk has first and second opposing ends and a closed curve wall extending between the first and second ends. At least one of the first and second ends serves as a boundary between the disk and a second dielectric material. A hole penetrates the disk from the first end and extends toward the second end. The hole exhibits a diameter less than 0.2 D. The resonator also includes a conductive coating on the disk wall and a dielectric tuning plug. The dielectric tuning plug has a dielectric constant less than 0.5∈r and extends into the hole in the disk. As a result, the tunable resonator has a lowest resonant frequency in a HE0xcex3xcex4 mode of oscillation.